Process of making a hard lining metal



Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE PROCESS OF MAKING A. HARD LINING METAL No Drawing. Application January 17, 1934, Serial No. 707,036

6 Claims.

This invention relates to hard lining metals for overlaying or lining steel and particularly for spinning into steel tubes, and the principal objects of the invention are to produce a lining metal of extreme hardness and abrasion-resisting qualities which will melt at a sufliciently lower temperature than the tube to be lined so as to avoid deformation of the same, also such a lining metal which will have an unusually low thermal conductivity, and a per fect bonding quality, all in a metal much cheaper than alloys of anywhere near equal hardness or wear-resisting properties heretofore used. Other features of the invention will appear in the following description.

Heretofore various hard metals have been used in lining steel tubes such as Stelllte and other hard alloys, applied with difficulty on account of their high melting points, and while the prior art shows some experimental work has been done to determine the effect of boron on iron and steel and it was known to impart hardness, yet the product of the earlier workers, was unsuitable for use as an extreme wear-resisting lining for steel tubes as it was not of suflicient hardness, and its melting point was too close to that of'a steel tube as to have required special revolving molds or supporting means for the tube, or the casting of the metal in molten condition into the tube. Boronized steel and iron have heretofore been made by melting with iron or steel a quantity of ferroboron sufficient to impart the desired boron content, and since commercial ferro-boron carrying about 20% of boron is produced by the Goldschmit alumino-thermic process and contains about 2 of aluminum this reduces the wear resistance of the steel or iron with which it is alloyed.

In carrying on extensive experiments with boron additions to iron and steel in an attempt to produce superior hard liners in steel and iron tubes we discovered that if instead of using iron and steel as heretofore always used for the major metal in the alloy, cast iron is employed as the major metal, its sulphur and phosphorus content kept very low and a boron addition made free from aluminum, that a superior hard metal resulted all out of line with boronized iron or steel as heretofore known.

Such a product as cast iron treatedwith boron has never been disclosed in the art or its properties known before our discovery insofar as we are aware. This cast iron product has much greater hardness than boronized iron or steel; it can not be machined, except by grinding; has great resistance to wear or molecular disruption from extraneous friction; melts at a considerably to sulphur.

lower temperature than boronized iron or steel, namely, about 1950 F. has the property of very low thermal conductivity, running to less than /5th that of ordinary iron or steel; has perfect bonding quality even without a flux; and, finally, 5 is more cheaply produced than any comparable hardlining alloy.

Lined steel tubes made with our improved hard lining metal have been produced in large numbers, and under exceptionally severe usage, such as for slush pump liners in the oil well industry, have shown a useful life of many times that of anything heretofore available.

In the production of our hard lining metal we select a grade of commercial cast iron pig containing three or more per cent of carbon, two to four per cent silicon, preferably under 0.05% of phosphorus and not over 0.1%, and the same as Such a cast iron pig is readily available in the market. Of this cast iron we take as an example '75 pounds, borax 5 pounds (commercial sodium tetraborate either lump or granular), and place in the bottom of a standard #50 plumbago crucible measuring about nine inches in diameter and twelve inches deep inside and composed of about half clay and graphite.

The crucible is placed in a suitable furnace preferably gas-fired on account of easier control and freedom from sulphur, and the crucible gradually brought up to heat until the charge is completely melted. This usually takes from %ths to one hours time. At this time ten pounds more of borax is added and the crucible covered with a fire-clay lid having a small vent in the center. Heating is then continued for about another hour and at which time the temperature should show about 2700 F. The crucible is then removed from the furnace, slag poured oil, and the molten metal run out on a large steel sheet to form a thin layer. When the cast metal layer is cool it is broken into small pieces about an inch across and then tumbled in a revolving tumbling barrel while air is blown through to carry away the dust and loosened matter so that the metal pieces are perfectly clean-and ready for use by placing in the steel tubes for melting therein to form the hard lining.

The metal produced'by the above process will analyze about as follows:

Per cent Carbon; 3.00 to 3.30 Boron 1.00 to 1.15 Silicon 1.00' to 1.5

Balance iron Any other elements originally present in small quantity will be substantially unaffected.

For metal not to be used immediately for liners,,

' gether with the silicon which aids in the reduction of the boron and which carbon is substantially replenished by absorption from the crucible if of about the proportional surface area to volume of charge content as given. The carbon con- ,tent could be maintained by adding carbon if clay crucibles were used. The size of crucible given also insures a sufficiently large area of molten metal being exposed to the borax to make the reduction of the borax take place effectively. Also to be considered in the initial presence of from 2 to 4% silicon as it also aids in the reduction of boron from borax.

The object in first incorporating but about a third of the required amount of borax in the charge is to avoid excessive effervescence which would cause considerable loss of this necessary ingredient. After the first hour's heating a violent boiling of the mass takes place due to the reaction of carbon and borax with liberation of CO, and hence the necessity of covering the crucible to avoid some loss of contents.

It has been found by experience that a phosphorus content in excess of 0.1% is detrimental to the final product insofar as its power to resist abrasion is concerned. Also that even a few per cent of aluminum is detrimental due to its soften ing effect on the metal, probably in causing precipitation of graphite. Sulphur tends to cause porosity.

The metal resulting from the above process is a cast iron of unusual properties not found mentioned in any of the art literaure with which we have become acquainted through diligent search. This metal melts at about 1950" F., and it is of great hardness, depending on the relation of the boron and carbon content, the latter of which should generally be maintained at a point about 3% of the iron by weight, though the useful range runs from about 2 to 4%, while a carbon content above 5% makes the final metal too brittle. The

. most useful range of the boron content runs from 0.2 to 2 Some of the properties of cast iron boronized in accordance with the process described are tabulated in comparison with plain cast iron in the following table:

Theamal con m:- 5 :35 333: tivity Hardness B. t. u./hr./ diamond m sq it of Brinell cast iron cast iron thickness 3. 42 0. 00 27. 450 3. 67 0. 09 20. 2 475 3. 51 0. 13 14. 0 600 3. 50 0. 22 7. 5 523 3. 43 X 0. 49 6.0 649 3. 2s 1 1.02 5. 2 705 3. 03 2 l. 70 4. 6 800 3. 00 2. 50 4.3 3. 00 5. 00 4. 2

7 It is to be understood that these alloys of the above physical properties contain about 1% silicon on the average. Variations in the silicon content may eifect some variation in the above properties. Its upper limit should not exceed 2 as in the increased percentages its tendency is to soften the metal by precipitating some of the car- 5 bon as graphite.

In forming the hard lining in steel or iron tubes or pipes we preferably crush the pieces of ourmetalas obtained from the tumbling barrel, introduce the desired quantity into the steel or 10 iron tube or pipe which has previously been pickeled or otherwise thoroughly cleaned, close the end or ends with a metal disk or plug which may be forced in, welded, or otherwise secured in place and which plug should have a minute vent for escape of gases or heated air. In some cases a small quantity of sodium carbonate, sodium borate, calcium fluoride, etc., may also-be introduced with the metal charge to pick up any non-metallics present, though if the tubes are properly cleaned this is not necessary.

The closed tube or pipe is then gradually and evenly heated while being slowly revolved in a suitable furnace until just above the melting point of the charge, quickly withdrawn from the furnace and at once placed between the centers of a spinning lathe and revolved on a horizontal axis at a speed of about 1000 or more peripheral feet per minute, for about a half minute more or less, and at which time it will have lost enough heat by radiation to freeze the charge of metal into a smooth even layer within the tube. After completely cooling, one or both ends of the tube may be cut open and the hard lining 7 ground to the exact dimension desired, and of course the outside of the tube may be machined in any manner'desired.

The linings may be very thin or extremely thick, and in any case they are a perfect bond so that sections of the lined article may be ruptured 40 without separation of the layer. The linings are adaptable to steel and iron pipes, tubes, engine and pump cylinders, internal brake drums, and all similar hollow articles.

When the linings are applied to explosive en- 4 gine cylinders, the exceptionally low thermal con ductivity minimizes the expansion under heat and consequent distortion so that exceptionally fine clearances may be maintained. The claims in the present case have been 5 covering the hollow, boron iron alloy lined articles are contained in a divisional case filed under Serial No. 741,996 on August 29, 1934.

Having thus described our invention what we claim is:

1. The process of making a hard lining metal 6 comprising the melting of cast iron of a carbon content from 2 to 5% in contact with borax and in presence of silicon and extraneous carbon and maintaining the mass in molten condition for a time period ranging from about an hour to several hours to cause absorption of boron by the cast iron to an amount ranging from 0.15% to 4% of the weight of the cast iron.

2. In the process of claim 1, first adding but a part of the required borax to the charge, and after melting adding the remainder of the borax and continuing the heating.

3. In the process of claim 1, first adding but a part of the required borax to the charge, and after melting adding the remainder of the borax walls and yield up its boron to alloy with the cast I and continuing the heating while substantially covering the reaction chamber holding the charge.

4. The process of making a hard lining metal comprising the melting of cast iron of a carbon content from 2 to 5% in contact with borax in a graphite crucible of relatively large surface area with respect to the charge whereby the borax may react with some of the carbon of the crucible walls and yield up its boron to-alloy with the cast iron.

5. The process of making a hard lining metal comprising the melting of cast iron 01' a carbon content from 2 to 5% in contact with borax in a graphite crucible of relatively large surface area with respect to the charge whereby the borax may react with some of the carbon of the crucible iron, said cast iron having a silicon content not over 2% and from a trace to no'more than 0.1% phosphorus.

6. The process of making a hard lining metal comprising the melting of cast iron 01 a carbon content from 2 to 5% in contact with borax in a graphite crucible of relatively large surface area with respect to the charge whereby the borax may react with some of the carbon of the crucible walls and yield up its boron to alloy with the cast iron, said cast iron having a silicon content not over 2'/ and from a trace to no more than 0.1% each of sulphur and phosphorus.

FREDERICK A. KORMANN. WALTER F. HIRSCH. 

